1. Field of the Invention
The invention relates to the field of solid state lasers and in particular to semiconductor lasers fabricated in noncubic materials such as GaN.
2. Description of the Prior Art
Metallic nitride in-plane lasers, such as indium nitride, GaN or aluminum nitride lasers, operating in the 300 to 700 nm range are potentially attractive devices for visible light applications and for high density data storage systems. Blue, green, and yellow high brightness, light emitting diodes (LED) have been fabricated. Recently, electrically pumped lasers have been demonstrated. Optically pumped GaN lasers have been made with high thresholds in the range of 100 to 800 kW/cm.sup.2 operating at room temperature. To reduce the lasing threshold, however, it is necessary that the mirrors in the lasers be improved. The most promising types of mirrors for use in an in-plane device are an etched distributed Bragg reflector mirror (DBR) and etched facet mirrors. However, the fabrication of both of these mirror types is difficult. First, it is difficult to create facets with reactive ion etching that are both smooth and perpendicular to the wafer surface. Second, reactive ion etching causes surface damage in GaN which is a problem for the performance of both DBR mirrors and etched facet mirrors.
Another possible type of mirror which could be chosen for GaN based lasers is a mirror made from a cleaved facet. With the application of high reflectivity coatings, cleaved facet mirrors are expected to provide comparable reflectivities to etched mirrors. Cleaved facet mirrors have been fabricated for GaAs grown on silicon carbide. See A. T. Ping et al., Appl. Phys. Lett. 67,1250(1995) However, cleaved mirrors have not been fabricated for GaN grown on sapphire because the cleavage planes of (0001) sapphire substrates are not perpendicular to the wafer surface.
Therefore, what is needed is a method for obtaining cleaved facet mirrors for GaN films grown on GaN, sapphire or other noncubic materials.